PHY 2054: Physics II
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Physics is like bicycle riding…..
About bicycle riding: If someone shows you
a trick, it means that,
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It is possible to do that trick
The person who showed you, can do the trick
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It does not mean that you can do the trick.
Try it a lot of times and you can too.
PHY 2054: notes a priori
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Please copy email to both of us.
Make sure, before the end of this week,
that Webassign works for you. Often
the problems are simple and
straightforward to fix. They become
more serious if they are not fixed right
away.
PHY 2054: Coulomb’s Law
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Recall
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Coulomb’s law
q1 q 2
F = k 2 rˆ
r
The direction is away, unless the charges
are different.
Forces are vectors, they add as vectors
F in Newtons, R in meters and q in Coulomb
PHY 2054: Coulomb’s Law
A rule
Try to calculate the force magnitude by ignoring
the signs of charges. Then assign the
direction by looking at the signs.
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Never do both (using the charge signs in the
calculation of the force and then assign the
direction).
PHY 2054: Coulomb’s Law
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The charge comes in units
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e = ± 1.6 x 10-19 C
1 C comes from the amount of charge
carried by a 1 Ampere current in 1
second.
The factor 9 x 109 is to fix the force
units
PHY 2054: Induction etc.
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Charges are
introduced
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by rubbing (depends)
Touching (same)
By induction
(opposite)
PHY 2054: Induction etc.
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Balls are touched and then separated. Rank
them by
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Charge left
Magnitude of Force before
After
Charge transferred
PHY 2054: Induction etc.
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Balls are touched and then separated. Rank
them by
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Charge left
Magnitude of Force before
After
Charge transferred 3,1,2
PHY 2054: HITT 1
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A circular ring of charge of radius b has a
total charge q uniformly distributed
around it. The magnitude of the electric
field at the center of the ring is
(c) keq2/b2
(a) 0 (b) keq/b2
(d) keq2/b
(e) none of these
PHY 2054: HITT 2
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Rank the magnitudes of the electric field at points
A, B, and C in the figure, with the largest
magnitude first. (a) A, C, B (b) A, B, C (c) C, A, B
(d) Can’t be determined by visual inspection
PHY 2054: Electric Fields
G
E=k
(z
qz
2
+R
)
2 3/ 2
zˆ